1. Field of the Invention:
The present invention relates to nozzle seals for sealing the nozzles of a nuclear steam generator vessel, and particularly to retraint means for securely holding the nozzle seal in place and preventing inward loosening and displacement thereof by high pressure in the nozzle.
2. Background of the Invention:
During refueling operations in a nuclear generating plant, it is desirable to simultaneously perform maintenance on the steam generator. To do this, the inlet nozzle of the steam generator vessel must be closed off. This is accomplished by use of a nozzle seal or dam which is installed in the nozzle from inside the inlet plenum of the generator vessel. One such nozzle seal is disclosed, for example, in copending U.S. application Ser. No. 605,354 filed Apr. 30, 1984, and entitled "Non-Bolted Ringless Nozzle Dam". Since work must be done within the inlet plenum, the nozzle seal or dam must be fully secured in the nozzle. While the nozzle seal is provided with an anchor assembly for anchoring it in place in the nozzle, nevertheless, this may be insufficient to insure that the nozzle seal will not be dislodged or displaced as a result of large pressure buildups within the nozzle, which could result in release of irradiated coolant from the reactor at great hazard to service and maintenance personnel.
It has been suggested that retention of the nozzle seal be accomplished by a restraint beam which essentially operates like a bar or beam wedged between the nozzle seal and the environmental ledge of the generator vessel. However, such a beam arrangement is quite heavy and difficult to install, resulting in large exposure times. Furthermore, its construction and manner of installation concentrates all the retaining force at a single location on the steam generator environmental ledge, creating a high risk area at that point. Furthermore, such a device does not readily accommodate manufacturing tolerances in the dimensions of the nozzle and the nozzle seal which result in variations in the seating location of the nozzle seal in the nozzle.